1. Field of the Invention
This invention relates to a rotary magnetic head device which is preferably applied to a digital VTR having several rotary magnetic heads (head tips) mounted thereon or the like.
2. Description of the Prior Art
It is well known in the prior art of the digital VTR that as the number of revolutions of the rotary drum is increased to perform a recording/reproducing operation or the number of recording/reproducing heads is increased to process the data in parallel to perform recording/reproducing operation so as to process a large amount of data. In case of a digital VTR in which high definition signals for use in reproducing high definition images are recorded or reproduced, a certain type of digital VTR employs the latter process.
In this type of digital VTR, the data rate to be recorded or reproduced reaches about 1 Gbps, so that eight magnetic heads are used as the rotary magnetic head device for recording/reproducing operation. FIG. 4 illustrates one example of an arrangement of the magnetic heads. In the case that the magnetic heads constructed of a plurality of head tips are fixed onto the rotary drum 2 (actually the rotary plate disposed between the upper and lower divided drums), that the plurality of head tips are equally spaced apart on the rotary drum 2 and disposed on it. However, this arrangement may cause a problem of a crosstalk of signals, so that as shown in FIG. 4, the magnetic heads are concentrically fixed at a part of the drum.
In FIG. 4, reference numerals 3 and 4 denote recording heads in which four head tips (Ra, Rb, Rc, Rd) and (Ra', Rb', Rc', Rd') are disposed adjacent to each other, respectively, and each of the heads may act as an independent recording head. The recording heads 3 and 4 are angularly spaced apart by about 180.degree. . Reference numerals 5 and 6 denote reproducing heads in which each of four head tips (Pa, Pb, Pc, Pd), (Pa', Pb', Pc', Pd') is disposed adjacent to each other in the same manner as that of the recording heads 3 and 4 and each of the heads any act as an independent reproducing head. As shown in the figure, the reproducing heads 5 and 6 are angularly disposed by about 180.degree. at a position shifted by 90.degree. from each of the recording heads 3 and 4.
Four head tips constituting the recording heads 3, 4 and the reproducing heads 5, 6 are formed as small as possible and an inter-head tip distance is made as small as possible to cause the four head tips to be mounted on the same head base (not shown). As described above, an entire mass and a shape of the head base are formed small to facilitate a manufacturing of the head and additionally it has an effect that a centrifugal force acting against the head base can be reduced during its use.
Each of the head tips (Ra, Rb, Rc, Rd), (Ra', Rb', Rc', Rd') and (Pa, Pb, Pc, Pd), (Pa', Pb', Pc', Pd') is fixed so as to be in parallel to each other and at the same time as shown in the figure, they are disposed to show the same length (a projecting amount).
As described above, when the magnetic head tips are used while they are disposed in parallel to each other and have the same projecting length (a projecting amount), the recording heads 3, 4 and the reproducing heads 5, 6 gradually wear. Since this wearing phenomenon is equally found in all the heads, only the recording head 3 will be studied. In this case, the four head tips do not uniformly wear, but the outer two head tips Ra and Rd wear more than the inner two head tips Rb and Rc. This is due to the fact that the outer head tips Ra and Rd have a higher surface pressure (a tape contact pressure) than that of the inner head tips Rb and Rc.
In addition, the outer head tips have a larger tape noise than that of the inner head tips and further it has been confirmed that the tape noise deteriorates as a ratio of S/N.